Effects of Temperature and Nutrients on Proteinase Production by Pseudomonas fluorescens and Ps. aeruginosa in Broth and Milk

Temperature and the composition of the medium influenced the production of proteinase by Pseudomonas fluorescens and Pseudomonas aeruginosa isolated from raw milk. Many isolates of Ps. fluorescens digested litmus milk at 10° but not at 5° or 2°. With Ps. fluorescens proteinase production per unit of growth in a Peptone–Yeast Extract broth declined progressively as the incubation temperature was reduced from 20° to 5°. At 30° there was heavy growth in the same medium but only slight proteinase production whereas enzyme production by Ps. aeruginosa was maximal at this temperature. Proteinase production by both species in semi‐defined media was essentially a function of the organic nitrogen content of the medium; there was evidence of catabolite repression by glucose and, to a lesser extent, lactate. In milks seeded with these pseudomonads, the extent of proteolysis was either increased markedly or slightly decreased when glucose was included.